Selenium (Se) is an essential micronutrient for animals and humans. In the food chain, the intake of Se by animals and humans depends largely on Se content in plants, whereas the major source of Se in plants lies in the soil. The objective of this thesis was to study the content, forms, plant uptake and fertilization of Se in agricultural soils in the Netherlands and underlying controlling factors and mechanisms, to provide guidance for soil testing and fertilization recommendation for efficient Se management in agriculture. Majority of agricultural soils (grassland and arable land) in the Netherlands contains low total Se (i.e. in the range of Se deficient), which is predominantly present in organic form. Only a small fraction of total Se is present as inorganic form and residual Se. The content of Se in soils in general increases with soil organic matter content. The amount of Se-rich dissolved organic matter and labile organic Se control Se plant uptake in soils containing Se-rich organic matter (e.g. potato arable land soils) and Se-poor organic matter (e.g. grassland soils), respectively, suggesting that land use influences Se availability in soils for plant uptake, probably via properties of Se-containing soil organic matter. Soil fertilization with Se (as selenate) increased significantly Se content in grass grown on different soil types, although the majority of Se in grass is still below the recommended amount for cattle intake upon fertilization. The effectiveness of Se fertilization has small differences among different soil types. Nevertheless, the effectiveness tends to be slightly higher on sandy soils than on clay soils and organic-rich soils. This thesis has shown the central role of soil organic matter in determining the amount, forms and availability of Se in the low Se Dutch agricultural soils for plant uptake.